1. Field
The present disclosure relates generally to inert gas welding. More particularly, the invention is directed to purge dams for retaining purge gas around a weld zone.
2. Description of the Prior Art
By way of background, inert gas welding is a species of arc welding in which the molten weld pool is shielded from atmospheric contamination and oxidation by bathing it with an inert gas, such as Argon, or a mixture of Helium and Argon. Popular examples of inert gas welding include TIG (Tungsten Inert Gas) welding and MIG (Metal Inert Gas) welding.
When welding together pipes and other enclosed structures using inert gas welding, it is important to purge the interior of the pipe or structure in the vicinity of the weld zone to prevent corrosion and the formation of oxides on the interior side of the weld pool. Purge dams are conventionally used for this purpose. For example, when butt-welding the ends of two pipe sections to form a consolidated pipe run, two purge dam structures are placed in the pipes, one in each pipe end on either side of the weld zone. A purge gas can then be introduced into the area between the purge dams.
Water degradable purge dams have been proposed that are made from water degradable paper. The advantage of water degradable paper purge dams is that they can be placed in close proximity to a weld zone, and then removed following welding by dissolving or otherwise degrading them with water introduced through the pipe. Insofar as pipe systems typically undergo hydrostatic pressure testing or flushing with water prior to use, water degradable purge dams can be used in many cases without any additional processing steps following welding. Such purge dams are typically formed from a sheet of water soluble paper that is formed into a concave shape in which a central portion of the purge dam spans across the diameter to the pipe to be welded and a peripheral edge portion of the purge dam engages the pipe wall so that it can be secured thereto, such as by applying a water degradable adhesive tape or glue at the installation site, or by pre-applying such an adhesive material during manufacture of the purge dam.
Applicant submits that there is presently a need for improvement in the construction of water-degradable purge dams. What is required in particular is a purge dam apparatus that can be installed in a pipe or other structure to be welded, and retained therein without the use of adhesives.